The invention relates to a reactor control rod system, particularly to a system for determining the time required for the control rods to move into their scram position, and more particularly to a fluid driven jet-edge whistle timing system for real-time detection of control rod movement.
The basic design of a reactor control rod system is such that the control rods are held by latches, or other means, in an up (out of core) position during normal reactor operation. The scram signal will trigger the latch opening mechanism and the rods will fall along the guide tube downward (into the core) under gravitational and hydraulic forces. The rods have to reach the bottom position (fully inserted into core) within a certain time in order to shut the reactor down safely. The real-time assessment of the timing of the control rods is an essential indication of whether the scram mission is completed or not. This timing is an important parameter in reactor safety, particularly in liquid metal fast breeder reactor (LMFBR) safety.
Various signal producing systems have been developed for monitoring nuclear reactors. For example, U.S. Pat. No. 4,020,693, issued May 3, 1977 in the name of F. F. Ahlgren et al. teaches a modified Galton whistle for nuclear reactor monitoring of the reactor temperature, etc. U.S. Pat. No. 3,237,150, issued Feb. 22, 1966 in the name of K. H. Beck et al., teaches an ultrasonic position indicator system for determining the position of control rods within the core of a nuclear reactor. U.S. Pat. No. 3,913,407, issued Oct. 21, 1975 in the name of M. Hanff et al. teaches an acoustic detection device for use in a nuclear reactor to sense the start of a boiling process in the reactor coolant liquid. U.S. Pat. No. 3,303,457, issued Feb. 7, 1967 in the name of J. A. Akesson, teaches a nuclear reactor control rod position indicator using a permanent magnet which activates an ultrasonic transmitter-receiver when the control rod drops. U.S. Pat. No. 4,064,451, issued Dec. 20, 1977 in the name of M. K. Foxworthy, teaches a control rod position indicator operating in a manner quite similar to the position indicator of above-referenced U.S. Pat. No. 3,303,457.
In addition to the above-referenced exemplary signal producing systems for nuclear reactors, other signal producing devices have been developed, such as exemplified by U.S. Pat. No. 2,971,491 issued Feb. 14, 1961 in the name of H. L. Yeagley which teaches a signal whistle system which emits supersonic vibrations and which can be readily adjustable in pitch; while U.S. Pat. No. 3,053,220 issued Sept. 11, 1962 in the name of H. E. Sawyer teaches an impact energized sound source. Ultrasonic jet-edge whistles are known in the art in various articles, as evidenced for example by J. Hartmann (1939) J. Sci. Instru. 16, p. 140; and by J. V. Bouyoucos et al. (1954), J. Acoust. Soc. Am. Vol. 26, No. 4, p. 511. The jet-edge whistle has been used by industry for emulsification and dispersion, high power sirens, ultrasonic drying, etc. Acoustic signal transmitting and processing systems are known in the art as exemplified by U.S. Pat. Nos. 3,548,648 issued Dec. 22, 1970 in the name of B. Weichbrodt et al., and 4,143,552 issued Mar. 13, 1979 in the name of D. E. Godfrey.
Due to the high temperature of the liquid metal (sodium) environment of the LMFBR core, no electronic device can be used in the core area to detect the timing. An ultrasonic or acoustic impact signal due to the bottoming of the control rod, which may be produced by the above-referenced prior art nuclear monitoring systems provide an indicator of the timing, with the acoustic signal being detected by sensors located on the top portion of the reactor where the environment is such that the sensor could survive. However, there are two difficulties associated with this approach. Firstly, impact (acoustic) signals have a rather broad band spectrum. The central frequency depends on the configuration of the two impacting bodies. In general, such a signal is in the lower frequency range, usually below 50 kHz. Whether one can detect this kind of broad band signal in the midst of the reactor background noise is very much in question. Secondly, when the reactor scrams, all the control rods will go down simultaneously. There will be many impacts within a very short time. To differentiate which impact signal is created by which control rod requires the development of a sophisticated spatial filtering processing technique. This would involve sizable computer facilities and a lengthy processing time. Thus, a need exists, particularly for an LMFBR, to provide an economical real-time timing measurement system for the control rods, either for the primary or the secondary control rod system.
Therefore, it is an object of this invention to provide an economical real-time timing measurement system for control rods in a nuclear reactor.
A further object of the invention is to provide a control rod timing system particularly adapted for liquid metal fast breeder reactors for measuring the time duration of each control rod during a reactor scram.
Another object of the invention is to provide a timing system for the secondary control rod system of an LMFBR which utilizes a high-frequency (above 100 kHz) pure tone acoustic signal.
Another object of the invention is to provide a fluid driven jet-edge whistle for providing real-time timing measurements for reactor control rods during a scram operation.
Another object of the invention is to provide a real-time timing measurement system which incorporates a fluid driven jet-edge whistle, a signal receiving system, and a signal interpretation circuit system.
Another object of the invention is to provide a fluid driven jet-edge whistle which functions to convert the kinetic and potential energy of the plunging reactor control rod into the kinetic energy of the jet thereby producing signals for real-time detection of the timing of the control rod in its scram operation.
Other objects of the invention will become readily apparent from the following description and accompanying drawings.